1. Field of the Invention
The present invention generally relates to a power supply apparatus that generates a plurality of power supply outputs and more particularly relates to a power supply apparatus that is capable of controlling a starting order and a stopping order of a plurality of power supply outputs.
2. Description of Related Art
A system that includes a plurality of ICs often needs a plurality of different power supply voltages. Further, power saving techniques such as reduction of power supply voltage by manufacturing process minimization are implemented in LSI such as microcomputer and ASIC, which raises the need for a plurality of kinds of power supply voltages in a single LSI.
Some of these LSI require starting and stopping the supply of power supply voltages in a predetermined order. For example, in LSI that requires two kinds of power supply voltages, e.g. 3.3 V and 2.5 V, the controlling order of the power supply voltages may be different between turn-on and turn-off, such as starting the supply of 3.3 V power supply voltage ahead of the other when turning-on the LSI and stopping the supply of 2.5 V power supply voltage ahead of the other when turning-off the LSI.
FIG. 3 shows the configuration of a power supply apparatus 30 that outputs two types of voltages as an example of the above system; i.e. a conventional power supply apparatus that supplies a power supply voltage to LSI or the like. A series regulator 31 steps down and smoothes a voltage supplied through a power supply input terminal 32 and outputs a prescribed output voltage V31 to a power supply output terminal 34. An ON/OFF signal terminal 33 is an input terminal of an ON/OFF signal for controlling the start and stop of the output from the series regulator 31. Similarly, a series regulator 35 steps down and smoothes a voltage supplied through a power supply input terminal 36 and outputs a prescribed output voltage V35 to a power supply output terminal 38. An ON/OFF signal terminal 37 is an input terminal of an ON/OFF signal for controlling the start and stop of the output from the series regulator 35.
In order to control the starting and stopping order of the output from the series regulators 31 and 35 in the power supply apparatus 30 of FIG. 3, it is necessary to input two types of control signals (ON/OFF signals) to the ON/OFF signal terminals 33 and 37. It is possible to differentiate the timing to start output and the timing to stop output between the series regulators 31 and 35 by inserting a delay circuit on an input line of the ON/OFF signal. Still, the starting order and the stopping order of the voltage output are the same in this case, and it is unable to implement the output start and the output stop respectively in opposite orders.
The power supply apparatus that is capable of starting the voltage output and stopping the voltage output in opposite order from each other by a single type of control signal is disclosed in Japanese Unexamined Patent Publications Nos. 10-224200 and 06-259171, which are respectively referred to herein as the related arts 1 and 2. According to the related art 1, when starting the power supply output, the power supply apparatus inputs one type of ON signal, latches the state of the ON signal into a flip-flop, and starts the output of the power supply for the first turn-on according to the output of the flip-flop. Then, it detects a change in the output voltage of the power supply that has been first to turn-on, latches the detected signal into a flip-flop for controlling the output of the second power supply and starts the output of the second power supply according to the output of the flip-flop. By repeating this operation, the apparatus starts the output of a plurality of power supply voltages sequentially. When stopping the voltage output, the apparatus latches the values into flip-flops for output control in the opposite order from the one for turn-on, thereby stopping the power supply output in the opposite order from the one when starting the output.
According to the related art 2, the power supply apparatus monitors a change in the output voltage generated in a plurality of voltage generators with an output monitor using a microcomputer and performs control so that the rise and fall of the outputs from the voltage generators are carried out in a prescribed order.
However, the power supply apparatus of the above related arts that are capable of controlling the starting order and the stopping order of a plurality of power supply outputs needs to use a flip-flop and a microcomputer.
Since the configuration described in the related art 1 controls the output sequence of a plurality of power supplies by using a flip-flop, it is necessary to input a clock signal for the operation of the flip-flop from an external device. This raises the need for a terminal for inputting the clock signal and causes an increase in an IC package size. The configuration also causes a noise on the output signal of the power supply apparatus due to the clock; thus, the configuration without the need for the clock signal is preferred.
The power supply apparatus of the related art 2 monitors a change in the output voltage generated in a plurality of voltage generators with an output monitor using a microcomputer and performs control so as to carry out the rise and fall of the output from the voltage generators in a prescribed order as described above. However, the use of the microcomputer causes large power consumption. It also causes an increase in an IC package size.